Tubes, corrosion

Tubing corrosion due to FIgS (sour corrosion) or COg (sweet corrosion) may become so severe that the tubing leaks. This would certainly require a workover. Monitoring of the... 

Most of the AHoy 600 outer diameter tube corrosion has occurred in the region of the upper tubesheet near the open lane, ie, an untubed lane across the middle of the steam generator (16,17). The steam carries entrained droplets of water through the open lane to the upper tubesheet region where the droplets dry out and concentrate the chemicals. Long tube inserts have been used to sleeve tubes in this region where wall defects have been detected. 

Steverding, B., Intergranular Sulfur Corrosion in Missile Thrust Chamber Nickel Tubes , Corrosion, 18, 433t (1%2)... 

Other gases which are occasionally present usually arise from pollution. Ammonia, which in various forms may be present in waste waters, attacks copper and copper alloys its presence in estuarine waters is one of the main causes of condenser-tube corrosion. 

Plate 1 illustrates what can be the consequences of a stress corrosion failure in a turbine and Plate 2 the consequences of two forms of boiler tube corrosion tube thinning and hydrogen embrittlement. The economic consequences of such problems and certain other areas where information on high temperature solutions is needed have been discussed elsewhere (6). 

Copper alloys are used extensively in power plant condensers, and as a result, copper can usually go into a corrosion product film or directly into solution as an ion or as a precipitate in the initial stages of condensation by tube corrosion. As corrosion products form and increase in thickness, the corrosion rate decreases until a steady state is achieved. Studies indicate that copper release is a function of flow rate more so than of the salt content of the makeup water. 

Water in reflux tends to get trapped in the tower, if the tower-bottom temperature is above the boiling point of water, at the tower s operating pressure. The water trickles down the tower and revaporizes off of the hot reboiler tubes. As the water may be saturated with corrosive salts and gases, reboiler tube corrosion can be rapid. In almost every petroleum refinery service, refluxing water is a quick route to reboiler tube leaks. 

Reaction vessels, spark plugs, electrical resistors, electron tubes, corrosion-resistant equipment, ball mills and grinders, food-processing equipment, piping, valves, pumps, and laboratory ware. 

When coal is burned in a combustion unit, mineral matter undergoes major changes that lead to problems of clinker formation, fly ash, slagging, and boiler tube corrosion. The efficiency of a combustion unit is related to the amount of ash produced, since it is a diluent. On the positive side, ash has been utilized as a construction material and is a possible source of refractory materials, as cement additives, or as adsorbents for gas-cleaning processes. However, the composition of the ash must be known before it can be utilized in this way. 

Liquid transmission and permeation through hose and tube Corrosion testing for gaskets Fluid resistance of gasket materials... 

H.A.Todhunter, Material Selection for Condenser Tubes, Corrosion, 11, 39 4 (1955). 

Often coal ash deposit effects are inter-related. For example, slagging will restrict waterwall heat absorption changing the temperature distribution in the boiler which in turn influences the nature and quantity of ash deposition in downstream convective sections. Ash deposits accumulated on convection tubes can reduce the cross-sectional flow area increasing fan requirements and also creating higher local gas velocities which accelerate fly ash erosion. In-situ deposit reactions can produce liquid phase components which are instrumental in tube corrosion. 

The location of equipment on site may also have an influence on the cleanliness of a heat exchanger from the point of view of fouling. For instance an air cooled heat exchanger placed where it is susceptible to particulate matter and dust, could lose efficiency due to fouling on the finned tubes. Corrosive fumes from nearby processing may also be responsible for air cooled heat exchanger fouling. 

The water chemistry of CANDU reactors embraces control of corrosion and corrosion-product transport in the coolant system, control of radiolytic decomposition of the moderator (51) and control of the concentration of soluble neutron absorbers used to adjust reactivity and control of boiler-water chemistry to minimize tube corrosion (52). The major chemical engineering effort has dealt with coolant technology and I will confine this review to that aspect of water chemistry. 

Under certain corrosive conditions, many metals form covering layers. If these are sufficiently dense, they act as protective films against the corrosive removal of the material. An example of this is the protective layer of iron oxide formed in unalloyed or low-alloy boiler tubes. Corrosion with erosion is understood as the combined action of mechanical surface removal and corrosion. With some soft and loose layers, the shear forces obtained with pure flowing liqnids at medium flow velocities are sufficient to damage the protective layer without the involvement of abrasive solid particles. Where drop impingement or cavitation is involved, the mechanical removal of material is understandable. 

A major drawback, however, is that the ash particles in the coal are raised to temperatures near 1400°C (2550°F) some mineral constituents will soften and glaze at these temperatures while others will volatilize. If the ash particles are still soft when they enter the convective heat-transfer part of the boiler, there is a possibility that they will form gluey deposits on the cooling tubes. Corrosive effects may also become more apparent at these high temperatures. 

Boiler tube corrosion and turbine blade erosion... 

Features of Ash and Slag Adhesion. The adhesion of ash and slag to the heating surfaces in boiler units is a serious detriment to good operation. Deposits on boiler tubes may interfere with circulation of the heat carrier, may bring about tube corrosion and rupture, may plug gas passages, and may reduce the boiler capacity. 

G. D. Bengough, G. Jones, and R. Pirret, Diagnosis of brass condenser tube corrosion, Journal of the Institute of Metals, vol. 23, pp. 65-137, 1920. 

Currently the major factors considered in the selection of a tube to be used in a pyrolysis furnace are the physical properties and the expected longevity of the tube. Corrosion and carburization certainly are of importance in this latter respect, but the surface activity should also be considered. Based on the present results, increasing the chromium content and decreasing the nickel content of the metal would reduce coking and other undesired surface reactions. A high chromium stainless steel would likely result in relatively few surface reactions. 

Ault, J. P., and Gehting, G. A., Statistical Analysis of Pitting Corrosion in Condenser Tubes, Corrosion Testing in Natural Waters Second Volume, ASTM STP 1300,1997, pp. 109-121. 

Primary Air Port Composite Tube Corrosion and Cracking... 

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